I. Field of the Invention
The present invention relates to a cannula device used as a medical instrument and to a medical bag provided with such a cannula device.
II. Description of the Prior Art
A needle of a syringe or a cannula which is connected to a fluid therapy bag or a blood transfusion bag, and which is pierced into the body of a patient as needed, generally comprises a hollow needle and a hub supporting the hollow needle at the proximal end portion thereof. The hub of the cannula which is most frequently used at present is made of a hard plastic such as polyvinyl chloride, and a hollow needle is inserted into the hub. In order to securely hold the hollow needle to the hub, a layer of a thermoset resin such as a cured epoxy resin is formed on the distal end plane of the hub to be integral with the outer circumferential surface of the hollow needle.
In order to protect such a cannula from damage due to an external impact until actual use, the cannula as described above is generally capped with a protector which is made of a hard plastic (generally a plastic harder than that of the hub). The protector comprises a hollow body whose one end is open and whose other end is closed. The hollow needle is inserted inside the hollow body. The outer diameter of the distal end portion of the hub is generally greater than the inner diameter of the open end of the protector by about 0.1 to 0.2 mm. Due to this difference, when the protector is placed over the cannula, the distal end portion of the hub is slightly reduced in diameter. Although the open end of the protector is slightly enlarged in diameter, the degree of enlargement is smaller than the degree of reduction in diameter at the distal end portion of the hub. The cannula, capped with the protector, is subjected to autoclaving sterilization.
If the epoxy resin for fixing the hollow needle to the hub is not completely cured in a cannula of the type as described above, the degree of reduction in diameter at the distal end portion of the hub upon being capped with the protector becomes too great. This substantially eliminates the difference in the outer diameter of the hub at the distal end portion thereof and the inner diameter of the protector, resulting in a poor hermetic or liquid-tight seal. This phenomenon is frequently made more pronounced by autoclaving sterilization. If a cannula device in this condition is connected to a bag holding an infusion solution or the like therein, the liquid which happens to be introduced into the protector from the bag through the hollow needle may leak to the outside through a contact portion between the hub and the protector. With such a cannula device, ambient air may also be introduced into the device through the contact portion between the hub and the protector, resulting in poor hygiene.
On the other hand, if the epoxy resin is excessively cured, any reduction in the diameter of the hub is difficult. If the protector is forcibly placed over the distal end portion of the hub, removal thereof is not easy. In addition, when the protector is placed over the device, the inner surface of the protector may be axially scratched due to the presence of too hard an epoxy resin layer. Since the diameter of the hub does hardly decrease, the scratches thus formed impair the hermetic or liquid-tight seal between the hub and the protector and present a similar problem as that encountered when the epoxy resin is not completely cured. This phenomenon is also made more pronounced by the heat of autoclaving sterilization.